1. Field of the Invention
This invention relates generally to security devices for door locks and in particular to a device which may be added to existing conventional-type cylindrical locks as being manufactured today. The device once added will positively prevent opening of the lock by any means and is completely tamperproof.
2. Description of the Prior Art
A common problem with known type door locks in that they can be tampered with, and entry may be gained by physically opening the lock by forcing the latch open through insertion of latch engaging members such as plastic cards or locksmith tools into the gap between the door and the door frame at the latch engaging point. Another method is to pick the lock itself as a substitute for a key and open the lock in this manner. Also, most security door locks may be opened if a person has a proper key. In many installations, it is very desirable that the lock be made unopenable by any means even by the use of a proper key.
Another problem with known type security door lock mechanisms is that they consist of barrel bolts, chain door fasteners, or other safety devices on the doors in addition to the key operated door lock. All of these types of security devices can be tampered with and defeated by anyone knowledgeable in the art of gaining forced entry.
Another problem with known type burglar resistant locks are that they require special and extensive modification of any existing type lock devices to which they are added or used. The fact that such additional security mechanism cannot be readily added and adapted to many existing type locks is a serious limitation to their acceptance in the field.
Another problem is the necessity for extensive modification of locks in order to install a security device of an extra nature and in the fact that if a defect or failure of some of the components occur, it is difficult and expensive to obtain repair or replacement parts.
Known prior art patents which may be pertinent to this invention are as follows:
U.S. Pat. No. 1,913,859, A. Sperduti, June 13, 1933;
U.S. Pat. No. 1,956,388, L. Kalina, Apr. 24, 1934;
U.S. Pat. No. 2,435,238, W. R. Schlage, Feb. 3, 1948;
U.S. Pat. No. 2,544,959, C. A. Hillgran, Mar. 13, 1951;
U.S. Pat. No. 2,623,279, C. L. Lucius, Dec. 30, 1952;
U.S. Pat. No. 2,942,449, C. White, June 28, 1960.
None of these known prior art devices offers the new and unique features of the invention disclosed herein.